Enhanced photodetection via π-bridge tuning and intramolecular non-covalent interactions in non-fused electron acceptors.

We report a systematic study of three fully non-fused ring electron acceptors (NFREAs): SN-1 (furan), SN-2 (thiophene) and SN-3 (EDOT). These molecules were designed to probe how π-bridge identity and targeted intramolecular non-covalent interactions control optoelectronic properties and photodetector performance. Cyclic voltammetry and thin film absorption confirm a clear trend in frontier energy levels and optical bandgaps (SN-3 shows the deepest HOMO and LUMO). Devices fabricated in an ITO/Molecule/Al architecture reveal that SN-3 combines favourable electronic coupling and conformational locking to give the best performance: responsivity R ≈ 0.0789 A W-1 (532 nm), estimated specific detectivity under shot-noise-limited approximations (D* ≈ 6.03 × 1013 Jones, 532 nm, 0 V), and a photocurrent-to-dark ratio > 106 under laser excitation. Under 1 sun the SN-3 device maintains D* ≈ 1.6 × 108 Jones. Time-resolved measurements show a fast photocurrent rise (t r = 4.37 s) and a long decay (t f = 29.5 s), consistent with rapid electron extraction (near-ideal LUMO-Al alignment) and slower hole removal (deep HOMO relative to ITO), together with trap-assisted carrier retention. Intensity dependence follows a super-linear power law (α ≈ 1.26 ± 0.16), supporting progressive trap filling at low-moderate incident powers and eventually becoming saturated as the power increases. Together, the results show that π-bridge selection can dominate device performance while intramolecular non-covalent interactions improve backbone planarity, providing a practical, solution-processable route to low-noise NFREA photodetectors.